Navegando por Autor "Oliveira, G. Pereira de"

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Incidence of planet candidates in open clusters and a planet confirmation
(EDPSCIENCE, 2018-12-10) Martins, Bruno Leonardo Canto; Leão, I. C.; Alves, S.; Oliveira, G. Pereira de; Cortés, C.; Brucalassi, A.; Melo, C. H. F.; Freitas, D. B. de; Pasquini, L.; Medeiros, J. R. de
Context. Detecting exoplanets in clusters of different ages is a powerful tool for understanding a number of open questions, such as how the occurrence rate of planets depends on stellar metallicity, on mass, or on stellar environment. Aims. We present the first results of our HARPS long-term radial velocity (RV) survey which aims to discover exoplanets around intermediate-mass (between ∼2 and 6 M ) evolved stars in open clusters. Methods. We selected 826 bona fide HARPS observations of 114 giants from an initial list of 29 open clusters and computed the halfpeak to peak variability of the HARPS RV measurements, namely ∆RV=2, for each target, to search for the best planet-host candidates. We also performed time series analyses for a few targets for which we have enough observations to search for orbital solutions. Results. Although we attempted to rule out the presence of binaries on the basis of previous surveys, we detected 14 new binary candidates in our sample, most of them identified from a comparison between HARPS and CORAVEL data. We also suggest 11 new planet-host candidates based on a relation between the stellar surface gravity and ∆RV=2. Ten of the candidates are less than 3 M , showing evidence of a low planet occurrence rate for massive stars. One of the planet-host candidates and one of the binary candidates show very clear RV periodic variations, allowing us to confirm the discovery of a new planet and to compute the orbital solution for the binary. The planet is IC 4651 9122b, with a minimum mass of m sin i = 6:3 MJ and a semimajor axis a = 2:0 AU. The binary companion is NGC 5822 201B, with a very low minimum mass of m sin i = 0:11 M and a semimajor axis a = 6:5 AU, which is comparable to the Jupiter distance to the Sun.
Kepler rapidly rotating giant stars
(American Astronomical Society, 2015) Costa, A. D.; Martins, B. L. Canto; Bravo, J. P.; Paz-Chinchón, F.; Chagas, M. L. das; Leão, I. C.; Oliveira, G. Pereira de; Silva, R. Rodrigues da; Roque, S.; Oliveira, L. L. A. de; Silva, D. Freire da; Medeiros, José Renan de
Rapidly rotating giant stars are relatively rare and may represent important stages of stellar evolution, resulting from stellar coalescence of close binary systems or accretion of substellar companions by their hosting stars. In the present Letter, we report 17 giant stars observed in the scope of the Kepler space mission exhibiting rapid rotation behavior. For the first time, the abnormal rotational behavior for this puzzling family of stars is revealed by direct measurements of rotation, namely from photometric rotation period, exhibiting a very short rotation period with values ranging from 13 to 55 days. This finding points to remarkable surface rotation rates, up to 18 times the rotation of the Sun. These giants are combined with six others recently listed in the literature for mid-infrared (IR) diagnostics based on Wide-field Infrared Survey Explorer information, from which a trend for an IR excess is revealed for at least one-half of the stars, but at a level far lower than the dust excess emission shown by planet-bearing main-sequence stars.

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Navegando por Autor "Oliveira, G. Pereira de"